The present invention generally relates to radiation emitter devices such as, for example, light emitting diode (LED) packages, and more particularly to opto-electronic emitter assemblies incorporating a plurality of optical radiation emitter devices.
As used herein, the term “discrete opto-electronic emitter assembly” means packaged radiation emitter devices that emit ultraviolet (UV), visible, or infrared (IR) radiation upon application of electrical power. Such discrete opto-electronic emitter assemblies include one or more radiation emitters. Radiation emitters, particularly optical radiation emitters, are used in a wide variety of commercial and industrial products and systems, and accordingly come in many forms and packages. As used herein, the term “optical radiation emitter” includes all emitter devices that emit visible light, near IR radiation, and UV radiation. Such optical radiation emitters may be pyrroluminescent, photoluminescent, electroluminescent, or other solid state emitter. Photoluminescent sources include phosphorescent and fluorescent sources. Fluorescent sources include phosphors and fluorescent dyes, pigments, crystals, substrates, coatings, and other materials.
Electroluminescent sources include semiconductor optical radiation emitters and other devices that emit optical radiation in response to electrical excitation. Semiconductor optical radiation emitters include light emitting diode (LED) chips, light emitting polymers (LEPs), organic light emitting devices (OLEDs), polymer light emitting devices (PLEDs), etc.
Semiconductor optical emitter components, particularly LED devices, have become commonplace in a wide variety of consumer and industrial opto-electronic applications. Other types of semiconductor optical emitter components, including OLEDs, LEPs, and the like, may also be packaged in discrete components suitable as substitutes for conventional inorganic LEDs in many of these applications.
Visible LED components of all colors are used alone or in small clusters as status indicators on such products as computer monitors, coffee makers, stereo receivers, CD players, VCRs, and the like. Such indicators are also found in a diversity of systems such as instrument panels in aircraft, trains, ships, cars, trucks, minivans and sport utility vehicles, etc. Addressable arrays containing hundreds or thousands of visible LED components are found in moving-message displays such as those found in many airports and stock market trading centers and also as high brightness large-area outdoor television screens found in many sports complexes and in some urban billboards.
Amber, red, and red-orange emitting visible LEDs are used in arrays of up to 100 components in visual signaling systems such as vehicle center high mounted stop lamps (CHMSLs), brake lamps, exterior turn signals and hazard flashers, exterior signaling mirrors, and for roadway construction hazard markers. Amber, red, and blue-green emitting visible LEDs are increasingly being used in much larger arrays of up to 400 components as stop/slow/go lights at intersections in urban and suburban intersections.
Multi-color combinations of pluralities of visibly colored LEDs are being used as the source of projected white light for illumination in binary-complementary and ternary RGB illuminators. Such illuminators are useful as vehicle or aircraft maplights, for example, or as vehicle or aircraft reading or courtesy lights, cargo lights, license plate illuminators, backup lights, and exterior mirror puddle lights. Other pertinent uses include portable flashlights and other illuminator applications where rugged, compact, lightweight, high efficiency, long-life, low voltage sources of white illumination are needed. Phosphor-enhanced “white” LEDs may also be used in some of these instances as illuminators.
Blue, violet, and UV emitting LEDs and LED lasers are being used extensively for data storage and retrieval applications such as reading and writing to high-density optical storage disks.
Opto-electronic radiation emitters and particularly LED devices are known to utilize more than one radiation emitter (i.e., LED chip). An example of such a structure is shown in FIG. 1. As illustrated, two LED chips 1 are mounted on a common electrical lead of a lead frame 2 and have wire bonds 3 attaching their other contact terminals to independent electrical leads of lead frame 2. An encapsulant 4 encapsulates the LEDs, wire bonds, and a significant portion of the leads so as to retain the physical integrity of the structure. As shown in FIG. 1, one end of encapsulant 4 has an outward-convex spherical surface 5 to serve as a lens at the light exit surface. The optical axis and focus of spherical surface 5 is typically centered between LED chips 1. Such an arrangement is problematic in that neither LED chip 1 is disposed at the focal point or on the central axis of spherical lens surface 5. This has the undesirable effect of magnifying and projecting an image of the LED chips at a distance from the LED device. Thus, if LED chips 1 emit light of different colors, a person looking directly at the LED device from a distance will clearly see two different color images of the LED chip point sources as magnified by lens 5. When the different colors from the LED chips are desired to mix so as to provide a different color, the ability of an observer to see the two different colored chips from a distance may render the device unsuitable for certain applications. For example, when a binary-complementary or ternary RGB chip set is utilized to provide effective white light for use as an indicator, a person looking directly at the indicator will see spots corresponding to the component colors of the device. When a binary-complementary or ternary RGB chip set is utilized to provide effective white light for use as an illuminator, the illuminator will project the magnified image of the differently colored LED chips such that the illuminating light is not uniformly white across the area of projected illumination.
The above imaging problem also can be present when one of the radiation emitters is an LED chip and the other radiation emitter is a photoluminescent material that is incorporated within the encapsulant or within a glob top over the LED chip. In such devices, the light emitted from the LED chip may not strike the photoluminescent material uniformly thereby exciting the photoluminescent material in a non-uniform fashion resulting in non-uniform light emission from the photoluminescent material. Further, the photoluminescent material may not be uniformly dispersed throughout the encapsulant thereby further exacerbating the problem.
U.S. Pat. No. 5,289,082 addresses the problem in utilizing two or three LED chips and proposes an encapsulant lens structure having elliptically segmented portions, with each portion aligned with respect to one of the LED chips and having its focal point at the corresponding LED chip position. While this approach may ameliorate the above problem, it nevertheless does not sufficiently overcome the problem so as to render a multi-chip LED device suitable for all applications where color mixing is required.
Accordingly, there is a need for an opto-electronic emitter device that includes a plurality of radiation emitters, whether electroluminescent and/or photoluminescent, that sufficiently disperses the light with a required intensity at a distance while not separating the images of the radiation emitters so as to create images of the two or three component colors.